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    <title>Document</title>
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    <script>
        /* 回调函数是一个异步处理过程 */
        var p=new Promise((resolve,reject)=>{
            resolve("success");
            reject("失败")
        })
        p.then(res=>{
            console.log(res)
        })
        console.log("4")
        /* 输出结果:
                   4  
                success */
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